This invention relates to micro-electromechanical devices, and more particularly to a method of analyzing and testing MEMS devices having one or more micromirrors.
A Digital Micromirror Device(trademark) (DMD(trademark)) is a type of microelectromechanical systems (MEMS) device. Invented in the 1980""s at Texas Instruments Incorporated, the DMD is a fast, reflective digital light switch.
The DMD has a variety of applications, such as imaging systems and optical switching. For imaging systems, the DMD is combined with image processing, memory, a light source, and optics to form a digital light processing system capable of projecting large, bright, high-contrast color images.
DMD""s may have a variety of designs, and the most popular design in current use is a structure consisting of a mirror that is rigidly connected to an underlying yoke. The yoke in turn is connected by two thin, mechanically compliant torsion hinges to support posts that are attached to the underlying substrate. Electrostatic fields developed between the underlying memory cell and the yoke and mirror cause rotation in the positive or negative rotation direction.
The fabrication of the above-described DMD structure begins with a completed CMOS memory circuit. Through the use of successive photomask layers, the structure is formed with alternating layers of metal for the address electrode, hinge, yoke, and mirror layers. Hardened photoresist forms sacrificial layers that are eventually removed to form air gaps.
Testing and development of DMD devices is facilitated by the ability to inspect the structure underlying the mirrors. In the past, the mirrors were removed using tape or epoxy. However, these methods of removal can break or contaminate the underlying structure, making it difficult to discern defects.
One aspect of the invention is a method of inspecting a target mirror element of a MEMS mirror device. First, one or more mirrors to be removed are selected. Then, a laser is used to remove the selected one or more mirrors. Once the mirror is removed, the underlying structure is visually available for inspection and for various types of analysis. Furthermore, because the laser removal of the mirror does not affect the operation of the device, the underlying structure can be observed in operation.
An advantage of the invention is that it provides a means for removing the mirror of a DMD other MEMS mirror device without affecting the underlying structure. This permits the underlying structure to be effectively analyzed and improved.